Command keys don't work on Desktop! Help!

Hi All-
weirdness...
OSX Tiger/G5 PPC /2 GHz dual/4Gig ram
suddenly today my "command-i" (get info on a file); "command-w" (close window) ,etc. AND my ability to click on a file name and rename it on the Desktop - has stopped working!! Computer crashed FCP (5.0.4) a few times editing the last few days (FCP seems OK - these key commands still work within the program)... HELP!! how do I restore this to normal!
Stu Aull
baffled in Alaska